1. Field of the Invention
The present invention relates to wireless communications, and more specifically, to channel scanning in wireless communications systems.
2. Description of the Prior Art
Wireless communications technologies are now highly developed. As a result, the popularity of wireless LAN usage is increasing. There are three most commonly seen wireless LAN specifications, IEEE 802.11a, IEEE 802.11b, and IEEE 802.11g. It is typical that wireless network cards available in the market are able to support at least one of the above-mentioned three specifications. When a laptop computer is connected to a wireless LAN, the wireless network card installed in the laptop must first scan for access points (AP) available for establishing connections in the area where the laptop is presently located. In general, the operating system of the laptop periodically sends out channel scanning requests to the wireless network card. Upon receiving the channel scanning request, the wireless network card scans all channels to determine whether there are channels and access points that are available for establishing connections with the wireless network card. The wireless network card then reports the scanning result to the operating system. Therefore, if one or more access points are available, the user or the operating system can further decide to which of the available access points the laptop should connect.
As the number of available wireless LAN specifications continues to increase, new wireless network cards are inevitably required to support more wireless LAN specifications. However, the various wireless LAN specifications may utilize different radio frequency bands, and as a result the channel ranges that the wireless network card needs to scan become broader accordingly. For example, the bands utilized by the IEEE 802.11a distribute at or around 5 GHz, while the bands utilized by the IEEE 802.11b distribute at or around 2.4 GHz; therefore, the corresponding channels are different. In general, a wireless network card cannot perform data transceiving operations while performing channel scan. Hence, when the number of channels is greater, data transceiving of the wireless network card must wait a longer time before the process of scanning channels completes. Only after scanning for channels has completed can the wireless network card continue with data transceiving. In addition, even when the operating system has not yet automatically sent out a channel scanning request to the wireless network card, but the user takes an affirmative action and controls the wireless network card to start performing the function of scanning channels, the wireless network card also stops transceiving data. Hence, the above-mentioned situation causes the data throughputs of the wireless network card being hindered and the performance of the wireless network card consequently suffers.